The present invention relates generally to medical catheters and leads, and more particularly implantable electrode leads for use with implantable cardiac pacemakers or other implantable stimulators.
The vast majority of electrode leads for use in conjunction with cardiac pacemakers, nerve stimulators and cardioverter defibrillators have had tubular lead bodies fabricated either of silicone rubber or polyurethane. Leads with tubular silicone rubber lead bodies are illustrated in U.S. Pat. No. 5,935,159, issued to Cross et al. and U.S. Pat. No. 5,584,873, issued to Shoberg et al. Leads with tubular polyurethane lead bodies are illustrated in U.S. Pat. No. 4,269,198, issued to Stokes and U.S. Pat. No. 4,355,646, issued to Kallok et al. Silicone rubber has the advantage of being extremely durable and biostable within the human body. However, even when wetted with blood, it is difficult to pass two leads with silicone rubber lead bodies down the same blood vessel, due to the high coefficient of friction of silicone rubber. In leads employing rotating conductors for advancement of helical electrodes, commonly referred to as xe2x80x9cscrew-inxe2x80x9d leads, the high coefficient of friction of silicone rubber makes efficient transfer of torque to the helical electrode more difficult.
There have been a number of techniques proposed to deal with this problem, including coating or lining a lead body with a material to reduce its coefficient of friction, for example as in U.S. Pat. No. 4,961,954 issued to Goldberg et al. or U.S. Pat. No. 5,358,517 issued to Pohndorf et al. An alternative is to treat the inner or outer surface of the silicone rubber lead body in some fashion to produce a lower coefficient of friction, for example, as disclosed in U.S. Pat. No. 5,830,329 issued to Stewart et al.
Both the above approaches have the disadvantage that they add complexity and cost to the process of manufacturing the silicone rubber lead body.
The present invention is directed to an implantable lead having a silicone rubber lead body that has a reduced coefficient of friction on an inner and/or outer surface thereof. The reduction in coefficient of friction is preferably accomplished by extruding a tubular lead body to define a plurality of small parallel longitudinally extending grooves on the inner or outer surface of the lead body. The grooves are preferably on the order of 0.5 microns to one millimeter in width and 1 micron to 20% of the wall thickness of the leady body in depth and are arranged around the internal or external circumference of the lead body relatively evenly spaced from one another. The grooves preferably have centers that are angularly displaced from one another by less than about 45 degrees, more preferably by less than about 20 degrees. The grooves are preferably sized so that they are spaced from one another no more than about 10%, preferably no more than about 5% of the external or internal circumference of the lead body. The grooves may be formed by means of a die having inwardly or outwardly directed projections that form the grooves during the extrusion process. Other methods of forming the grooves may also be employed. The formation of the grooves during extrusion provides a lead body having a lower coefficient of friction without the necessity of additional manufacturing process steps and without additional manufacturing costs.